If you are sleeping in the house now, or about to, the room you sleep in is not a leftover. It is the one place in the day that is supposed to be yours, and it is probably the place you have never measured. Sit on the bed you have, look around, and decide whether it holds the sleep you need.
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Measure the bed you will actually use
Measure the bed you are bringing, not the one in the catalog. Write down the footprint, then the clear space you need on the side you get out from, and the walk from that side to the door. Put tape on the floor so you can see the path with the furniture in place. If you cannot walk it in the dark without turning sideways, the room is too tight for a bed and a second person's routine, and you should know that before the mattress arrives.
Check the bed height too. If you will be getting up quickly during the night to hear a call or check on your parent, a bed that sits too low or too high will slow you down every time. Sit on the edge and stand up three times. Notice whether you have to push off the frame or the mattress to get your feet under you.
Check the door and the sound
Ask three questions about the door. Does it open into the room or out into the hall, and does the swing clash with the dresser or the closet? Can you close it fully without a fight? And if you use a lock, can someone open it from the outside in an emergency? A lock is a reasonable choice for your privacy, but only if the other side of the door has a way in.
Then stand in your bed spot with the door closed. Can you hear your parent's room, the bathroom, or the front door? If you need a monitor or a bell to hear a call, place the receiver where it reaches your pillow, not on the dresser across the room. Test it with the door closed and with the fan running, because that is the sound you will actually sleep through.
Count the outlets and the steps at three in the morning
List what needs power in this room: your phone, a monitor, a plug-in light, perhaps a heater or a fan. Count the outlets within reach of the bed. If you need a power strip, check that the cords do not cross the walkway you just taped out. A cord across the floor at night is a hazard you should fix on paper before it happens.
Walk the route you would take at three in the morning to reach the nearest bathroom and your parent's door. Count the steps. Note whether the path is lit without you having to hunt for a switch, whether anything sits in the way, and whether a rug edge lifts. The route you take half asleep is the one that counts.
Decide what moves in and what stays out
A spare room often becomes storage for everything the house no longer knows where to put. Make a rule before you move in. Your clothes, your charger, one lamp and whatever you need to sleep go in. Supplies, boxes and the parent's overflow do not. Give yourself one drawer and one shelf that nobody else touches, and say so out loud to the people who share the house.
You are allowed to have a room that feels like yours even while you are on duty. Closing the door is not selfish. It is part of what keeps you able to do the work tomorrow.
Write down what you found
Put the measurements, the door answers, the outlet count and the route steps on one page, and keep it with the rest of your planning papers. If the room changes, if the bed is replaced or the parent moves to a different floor, you will want the numbers you already checked instead of starting from memory at 2am.